A lithium nickel mixed metal oxide is used as a positive electrode active material of nonaqueous electrolyte secondary batteries such as lithium secondary batteries. Lithium secondary batteries are being used as compact power source for cell phones, notebook computers and the like, and it has been also attempted to further use lithium secondary batteries as a large-sized power source in automobile applications, power storage applications and the like.
As a positive electrode active material of nonaqueous electrolyte secondary batteries, a lithium nickel mixed metal oxide, which is obtained by calcining of powder obtained by mixing a mixed metal hydroxide which contains Ni and another transition metal element(s) such as Co and a lithium-containing compound, is often used. Examples of the method for the above-described mixing include wet methods in which mixing is carried out in a wet state and the solvent is then evaporated (for example, see WO 02/073718 A1) and dry methods in which mixing is carried out using a ball mill (for example, see JP 8-222220 A).
As described above, there are a variety of known mixing methods. However, it has not been determined yet what kind of mixed powder is suitable as a lithium nickel mixed metal oxide raw material. In addition, the discharge capacity of a nonaqueous electrolyte secondary battery in which a lithium nickel mixed metal oxide obtained by calcining of conventional powder is used as a positive electrode active material is still not sufficient.